First of all, Frost Titan tapped down permanents, not just creatures, and could do so upon entering the battlefield and while attacking. You also had a big 6/6 body that cost 4UU to cast, only one mana more than Icefall Regent. Plus, while the Regent is tricky to target with opponent's spells by requiring an extra cost of 2 colorless mana, the Titan could stifle abilities, too.
So how much does being a 4/3 flying Dragon make up for these deficiencies? The Regent is only a rare, first of all, so we can't expect the power level to be the same here. But a Frost Titan Dragon would have been pretty awesome.
Icefall Regent should be very good in Limited and could see some Standard play during its time, as well. It does die to Anger of the Gods, which doesn't target. To its credit, other removal becomes expensive when trying to take it down. Being a 4/3 in the air in a Control build is very good, but restricting its tap ability to only creatures, especially as it can only use that ability upon entering, limits this card's overall value.
At the very least, the Regent will help your tempo a bit, especially if it can help force some damage through and force your opponent to spend a bit extra to remove it from the board. It's decent enough to be considered for Constructed play, but I think even in Commander, it will only be played where a Blue Dragon might be needed, like in Intet, the Dreamer or Ojutai, Soul of Winter/Dragonlord Ojutai led builds. It's just hard to get excited about this card, but some tempo players might play it.